Solid state lighting is rapidly expanding its penetration, bringing to the market increased lighting efficiency, longer life and additional capabilities. One example of solid stage lighting is the use of light emitting diodes (LEDs), which are available in a plurality of colors. By combining the optical output of a plurality of colored LEDs a range of colors may be output. In one non-limiting example, the use of red, green and blue LEDs placed in proximity and behind a diffuser enables a complete range of colors by adjusting the relative intensity of the constituent LEDs, while the overall intensity of the constituent LEDs may be further adjusted to control the average overall luminance.
In order to economically control a large plurality of LEDs together producing sufficient light, the LEDs are typically supplied as a serially connected LED string, thereby sharing a single current. Each of the LED strings may be intensity controlled by one or both of amplitude modulation (AM), in which the value of the current through the LED string is adjusted, and pulse width modulation (PWM) in which the duty rate is controlled to adjust the average intensity over time. Thus, total intensity and color may be controlled by any combination of AM and PWM.
Solid state lighting exhibiting the ability to produce a plurality of colors over a range of intensities is preferably provided with a control unit arranged to enable user selection of both intensity and color. In a typical domestic arrangement, such a control unit is preferably arranged to be installed without requiring a professional electrician at a user convenient location; typically replacing an existing switch or dimmer. Such an arrangement limits communication between the control unit and the solid stage lighting unit to be over existing power wires or to be wireless. The use of wireless communication is often inconvenient due to interferences or increased cost, and similarly the use of communication over power wires is expensive.